The British navy said Wednesday that is ramping up measures to protect its waters from secret Russian operations after identifying a Russian spy vessel in UK waters for the second time in weeks.

Britain’s defence minister has warned Russian President Vladimir Putin that “we will not shy away from robust action” after telling Parliament that a Russian spy vessel had been operating in UK waters this week.

The Royal Navy has been monitoring a Russian spy ship after it was spotted around UK waters earlier this week, the defence secretary has told MPs. John Healey said the vessel, Yantar, was used for gathering intelligence and mapping the UK's critical underwater infrastructure.

NATO has been ramping up its forces along its eastern flank with Russia, Belarus, and Ukraine, deploying thousands of troops and equipment to deter Moscow from expanding its war into the territory of any of the organization’s 32 member countries.

NATO Secretary-General Mark Rutte warned that restoring the alliance's credibility after a Russian victory in Ukraine could require trillions of dollars.